Zwoegerziekte virus, the causative agent for progressive interstitial pneumonia (maedi) and meningo-leucoencephalitis (visna) in sheep.

The final results of experimental infections with virus recovered from the lungs of sheep suffering from progressive interstitial pneumonia (=zwoegerziekte=maedi) are reported. The virus could be reisolated from blood samples of all experimentally infected sheep. Every animal produced antibodies against the virus. The neutralising, complement-fixing and precipitating antibodies remained present in the blood for six years. Fourteen out of 21 intrapulmonarily infected sheep developed clinical and/or histopathological lung lesions and in three a meningo-leucoencephalitis was detected in addition. One of these three developed the clinical and pathological signs of 'visna' 14 months after inoculation. Signs of visna were seen in eight of 10 sheep that had been inoculated intracerebrally. Furthermore, nine of these sheep suffered from progressive interstitial pneumonia. Hence the name maedi-visna virus is proposed for the agent which causes both disease entities. Three sheep that yielded virus after infection and in which antibodies were detected, did not develop histopathological lesions.